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A fully integrated system that combines extended gate field-effect transistor (EGFET)-based potentiometric biosensors and electrochemical impedance spectroscopy (EIS)-based biosensors has been demonstrated. This integrated configuration enables the sequential measurement of the same immunological binding event on the same sensing surface and consequently sheds light on the fundamental origins of sensing signals produced by FET and EIS biosensors, as well as the correlation between the two. Detection of both the bovine serum albumin (BSA)/anti-BSA model system in buffer solution and bovine parainfluenza antibodies in complex blood plasma samples was demonstrated using the integrated biosensors. Comparison of the EGFET and EIS sensor responses reveals similar dynamic ranges, while equivalent circuit modeling of the EIS response shows that the commonly reported total impedance change (DZtotal) is dominated by the change in charge transfer resistance (Rct) rather than surface capacitance (Csurface). Using electrochemical kinetics and the Butler-Volmer equation, we unveil that the surface potential and charge transfer resistance, measured by potentiometric and impedance biosensors, respectively, are, in fact, intrinsically linked. This observation suggests that there is no significant gain in using the FET/EIS integrated system and leads to the demonstration that low-cost EGFET biosensors are sufficient as a detection tool to resolve the charge information of biomolecules for practical sensing applications. [ABSTRACT FROM AUTHOR]

Vertical tunnel diode arrays made from multiwall carbon nanotubes (MWCNTs) have shown recent promise for developing a practical optical rectenna, which is a device to convert electromagnetic waves at optical frequencies to direct current. Realizing an optical rectenna requires an antenna to be coupled to a diode that operates on the order of PHz (switching speed on the order of fs). Previously, we have demonstrated an optical rectenna device by engineering MWCNT–insulator–metal (MWCNT–I–M) tunnel diodes at the tips of vertically aligned MWCNT arrays, which act collectively as the antenna. However, the high electrical resistance of the MWCNT–I–M diode must be reduced to enable improved impedance matching between diode and antenna, which limited the rectified power in our prior work. Here, we address this issue of impedance mismatch through a series of experiments designed to elucidate contributions to the total electrical resistance of the device. Different combinations of metals, and metal and insulator thicknesses were tested for reduced contact resistance, while maintaining a working diode. Another development toward reducing resistance was to open MWCNT tips using oxygen plasma, which exposed multiple walls for bonding rather than just outer wall of closed tip CNTs. These developments were combined to reduce zero-bias resistance of MWCNT–I–M diode arrays to as low as 100 Ω ·cm2, which is 75 times lower than in our previous report. [ABSTRACT FROM PUBLISHER]

A high performance laccase-based biofuel cell cathode is developed using carbon nanosheets (CNS) as the catalyst support and buckypaper (BP) as the substrate electrode. Compared to multiwalled carbon nanotube (MWNT)-based electrodes, CNS-based electrodes exhibit better electrochemical properties for the oxygen reduction reaction (ORR) under biologically relevant conditions. It is shown that CNSs are conformally coated on the nanotubule bundles within the BP and that laccase is intimately attached to the CNS-BP. Electrochemical characterization is carried out to derive the kinetic parameters of the ORR at the laccase-CNS-BP cathode. The laccase-CNS-BP exhibits a steep ORR cathodic wave with a Tafel slope of 19 mV decade-1. The onset potential obtained for laccase ORR at CNS-BP is 20 mV higher than that of the MWNT-based electrodes, and the laccase-CNS-BP cathode has a higher current density than MWNT electrodes. [ABSTRACT FROM AUTHOR]